The purpose of this study is the clinical and genetic characterization of individual patients and kindreds with parathyroid cancer, germline CDC73 loss of function mutation, FIHP, and HPT-JT with the goals of defining the clinical spectrum of disease, searching for potential genotype-phenotype correlations relevant to mutation of known genes, and identifying new genes whose germline mutation predisposes to FIHP and related syndromes. Human research subjects included patients admitted to the NIH Clinical Center on Metabolic Diseases Branch and related protocols as well as qualified offsite patients. Gene mutational analysis, biochemical testing of blood and urine, culture and testing of isolated peripheral blood leukocytes, and imaging using plain X-rays, CT and MRI scanning, and nuclear medicine studies were used to characterize patients. Some patients were characterized during one or a few visits, while members of selected kindreds were followed longitudinally over years.